Is there any impact of connecting blocking diode in series with strings, over the I-V characteristics of solar PV array under non-uniform illumination?
I don't see why you want to put a blocking diode in series with the string, unless you have a lot of strings in parallel and want to minimise their interaction. In general anything in series with a string will make it worse, as it will lose volts. Partially shaded strings are difficult to work with as their IV curves are very different from fully irradiated strings. They can also show more than one local power maximum. Exactly what is it that you are trying to achieve?
It is only the case when large solar array is under partial shadow and we want to minimize the interaction between the strings. But the question is ...will there be any circulating current amongst the strings under partial shadow in the absence of blocking diode.
Are you asking about a blocking diode to prevent current from flowing into a branch, or a bypass diode to let current flow around shaded cells in a series string? This link provides a good overview of both diodes and the performance of a panel under nonideal conditions. http://www.solar.udel.edu/ELEG620/13_PV_modules.pdf
Kusum, besides all the theories please check the weak light shape of your module IV curves. Does the MPP voltage move significantly to lower values? If not, you must not worry about parasitic currents. Without blocking diods you may measure such parasitic currents at open circuit conditions. They wont harm your modules. Depending on the number of parallel strings, the given irradiance and the voltage mismach at between the strings you may measure in certain strings up to few amps.
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